A Stanford University author, I. M. Kroo reports that the quest for energy-efficient aircraft has renewed interest in canard configurations. These forward mounted airfoils, when used on rockets brings radially controllable forces to the front of an airframe (Ref: Journal of Aircraft Vol. 19 No. 9 1982 pp 792-793 and citation 155 of PB94-867116 of Dept. of Commerce NTIS.)
The Lockheed Electronics Company has developed an on-Board Structural Computer (OBSC) that monitors cyclic stresses on critical aircraft components. The system consists of an on-board processor that collects and processes data from strain gauges and from the aircraft's existing airspeed, altitude and vertical acceleration transducers (Ref: Citation 22 of PB94-8677116 NTIS)
The Information Services in Mechanical Engineering Database (ref: PB94-876851 of NTIS) cite 27 articles dealing with unwanted oscillation in aircraft from their selected technical journals, books and published proceedings. Unwanted oscillations contribute to excessive vibration, stress damage and fuel consumption.
Spoilers are little-mentioned in this selection of airfoil information from academic and research journals. However, lift-killing spoilers are used extensively to influence aircraft attitude and to manage flight energy.
Spoilers with manual adjustment are common control features for sport gliders (U.S. Pat. No. 2,410,855 Koppen). Power-actuated spoilers larger aircraft (U.S. Pat. No. 3,618,878) are also common. Hydraulically-actuated hinge-spoilers kill lift to quicken altitude descents without overspeed, and to shorten ground braking distance.
Spoilers provide easy access to energy in Bernoulli lift forces. Whenever airfoil shapes accelerate the air passing them, resistance incurred by the acceleration induces a force vector that is perpendicular (normal) to accelerated airflow. Spoiler action puts an airfoil barrier to acceleration. Ser. No. 07/935,284, now U.S. Pat. No. 5,495,396, uses spoilers to moderate and release fields of force that are perpendicular (normal) to observed airflow. e.g. Killing lift on one surface of a symmetrical airfoils releases normal force from the other surface.
A problem in full utilization of the force-releasing capability of spoilers is that they are too slow and too big. The usual mass, axis-of-rotation and actuating means for a spoiler's large surface area makes it actuating frequency too slow to be useful in damping Karman and other oscillations.
A related problem for quickly acting spoilers is an appropriate feedback sensing and data processing means to make a rapid spoiler useful.
A geometry problem in full utilization of Bernoulli lift effect of spoilers is that they are not curved. For instance, movement of the near-spherical nose section of subsonic aircraft invests instant energy in accelerating air particles over curved rings of expanding airfoil cross section. These balanced lift forces of Bernoulli physics are not presently used to augment flying-speed control of aircraft attitude or to minimize structural loads in aircraft.